1. Field of the invention
The present invention relates to a magneto-optical head for writing data to and-reading data from a magneto-optical disk. The invention also relates to a magneto-optical disk drive provided with such a magneto-optical head.
2. Description of the Related Art
JP-A-2003-51144, for example, discloses a magneto-optical head used for recording data by magnetic field modulation. The disclosed magneto-optical head includes an optical lens for forming a light spot on a data storage disk, a coil arranged between the lens and the disk for generating a magnetic field, and a magnetic element arranged between the coil and the lens. The coil generates heat when a current flows through the coil. For dissipating the heat, the magneto-optical head is provided with a heat sink surrounding the coil. With this structure, it is possible to prevent the lens from overheating due to the heat of the coil. Thus, the refractive index of the lens remains constant, whereby a proper light spot can be formed. When the disk rotates, airflow is caused between the disk and the MO head, which contributes to the cooling of the heat sink.
In the magnetic field modulation recording system, a high-frequency current of e.g. 50 MHz flows through the coil for magnetic field generation. When a magnetic field is generated by the coil, the magnetic flux passes through the heat sink around the coil. As the direction of the magnetic field is reversed at high frequency, eddy current is generated at the heat sink. The amount of eddy current generated depends on the distance between the outer circumference of the coil and the heat sink. Specifically, the amount of eddy current increases as the distance between the heat sink and the coil decreases and the amount decreases as the distance increases.
When the distance between the heat sink and the coil is relatively small, the heat sink can effectively dissipate the heat generated by the coil. However, the loss due to the eddy current deteriorates the generation efficiency of the magnetic field. On the other hand, when the distance between the heat sink and the coil is relatively large, the generation of eddy current at the heat sink is reduced, so that the generation efficiency of the magnetic field improves. However, the amount of heat dissipated by the heat sink is reduced.
The deterioration of generation efficiency of the magnetic field necessitates the use of a complicated system. Specifically, for example, the current value need be adjusted in accordance with the eddy current loss or the increase of frequency. On the other hand, when the heat dissipation effect lowers, the a proper light spot fails to be formed due to the change of the refractive index of the lens, as described above.